Railway circuits are known for detecting the presence of a vehicle travelling along the railway line comprising:
a first signal generator suitable for generating an alternating signal V(t) with varying voltage supplied to a first conductor which comprises rectilinear sections arranged adjacent to respective portions of a first and a second rail to define at least a first square coil magnetically coupled with the first and the second rail;
a signal receiver suitable for receiving the alternating signal V(t) present on the railway by means of a second square coil comprising a second conductor which comprises rectilinear sections arranged adjacent to respective portions of the first and second rail and magnetically coupled to the rails; the signal receiver is suitable for discriminating between two states:
a condition of signal received above a threshold in which the rails are not short-circuited by an axle of the vehicle and the railway circuit is considered free; and
a condition of signal received below a threshold or null in which the rails are short-circuited by at least one axle of a railway vehicle present on the railway and the railway circuit is considered occupied.
A railway circuit of the type described above can be—for example—equipped using the devices P-1400 of the company Railroad Control Limited in accordance with U.S. Pat. Nos. 5,936,551; 6,087,964; 6,226,575; and 6,281,809.